The four-band bulk Hamiltonian for a topological insulator, given in Reference [1]} is given by
\(\mathbf {H}(\mathbf {k})= &~\epsilon _0 (\mathbf {k})\mathbb {1}_2\otimes \mathbb {1}_2 + M(\mathbf {k}) \mathbb {1}_2\otimes {\sigma }_{{3}} \\&+ A_0 k_x {\sigma }_{{1}} \otimes {\sigma }_{{1}} + A_0 k_y {\sigma }_{{2}} \otimes {\sigma }_{{1}}\\&+ B_0 k_z {\sigma }_{{3}} \otimes {\sigma }_{{1}},\) 
